Retrofit with membrane the

Paraffin/Olefin separation

A. Motelica

O.S.L. Bruinsma

R. Kreiter

M. den Exter

J.F. Vente

October 2012

ECN-M--12-059

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Abstract

Olefins, such as ethylene, propylene, and butadiene, are among the most produced

intermediates in petrochemical industry. They are produced from a wide range of

hydrocarbon feedstocks (ethane, propane, butane, naphtha, gas oil) via a cracking

process. The last step in this process is the separation of olefins from other

hydrocarbons, which is traditionally performed with distillation. As the physicochemical

properties, such as volatility and boiling point, of the compounds are very similar, the

purification becomes capital and energy intensive. For example, the top of an

ethylene/ethane distillation column needs to be chilled to –30 oC and this requires large

amount of electric energy consumption. The separation of butadiene from the C4-

fraction is performed with the aid of an additional solvent. This solvent has to be

regenerated at the cost of additional high temperature steam. To overcome these

separation disadvantages of olefin/paraffin separation, different separation methods

have been investigated and proposed in recent years. Suggested options are based on

better heat integration of the overall process, or on novel separation systems such as

Heat Integrated Distillation Columns, membrane separation, adsorption-desorption

systems or on hybrid separation methods, for example, distillation combined with

membrane separation.

The focus of the current presentation is on integration of membrane-based gas

separation with conventional distillation. The aim is to find the minimum required

membrane performance, like selectivity and permeability, for an economically

attractive process. The separation of ethylene from ethane and butadiene from a C4-

mixture are considered as the most representative separation cases. The case of

propylene/propane separation is not considered due to mild temperatures (~30 oC) at

which this column is typically operated. In addition, the option to debottleneck existing

distillation columns for ethylene/ethane separation, with the aid of membrane, is

presented as new possible application of membranes.

The results reveal that for a hybrid system, membrane-distillation, the energy saving

potential for the separation of ethylene from ethane, if compared to the conventional

distillation, is rather low due to required very high membrane selectivity. The savings in

energy can be expected when the membrane selectivity for ethylene is > 60 (at this

moment the best reported membrane selectivity for ethylene is 12). However, this

study reveals that the possibility to debottleneck the column capacity in an existing

ethylene plant by using membranes is very high (see Figure 1 below). This is

economically attractive if the membrane has selectivity for ethylene ≥ 10. The reason

for good economic perspectives is the high price of polymeric grade ethylene. In case of

butadiene separation, the energy savings can be as high as 30% depending on

membrane selectivity and selected process configuration. This high value can be

reached when the membrane selectivity for butadiene relative to saturated

hydrocarbons equals 15. Similar to ethylene separation case, an increase in the

production capacity of butadiene can be achieved in an economic viable fashion.

ECN-M--12-059 3

Figure 1: Production capacity of a hybrid system (membrane + distillation) compared to the base case

process (conventional distillation) for different ethylene permeances

www.ecn.nl

Retrofit with membrane

Olefin/Paraffin Separation

Anatolie Motelica

Euromembrane 2012

London, 26 September 2012

Why retrofit Olefin/Paraffin?

Source: Oil & Gas Journal, Apr. 23 (2001)

Demand projections made in 2001 up to 2012

Between 2000 – 2010• an average increase with 4 mtpy

• or 4.3 % annually

Actual

capacities

Expectation beyond 2012• an increase with 1 to 5 mtpy

Global ethylene demand and capacity

147. 5 mtpy ethylene in 2012

Why Olefin/Paraffin separation?

• The most energy intensive processes Current global energy consumption1: 3000 – 4000 PJ/yr

(1 PJ = 30 mln Nm3 of Natural Gas) ~25 GJ/ton

30% – is the theoretical minimum

28% – Cracking process

22% – Separation

15% – Fractionation & Compression

Recent startup of the largest ethane cracker - 1.5 mtpy

ethylene, $1.3 bn (Source: Hydr. Proc. 2012).

• Difficult separation Close boiling components, Cryogenic Separation, Need for

Compression

• The most capital intensive processTall columns, Large compressors and Heat exchangers

• The most produced chemicalsin 2012 Ethylene: 147 mln tpy; Propylene: 77 mln. tpy; Butadiene: 14 mln. tpy

• Expected grow in demand in the next decades (2 to 4 % per year) driven by developing regions in Asia, Middle East and Latin America

1 Ren et al., (2006), Energy, 31, p.425-451

Olefin Plant

Cracking

Water

Quench

Compression

Drying ad

chiling

Dem

eth

aniz

er

Depro

paniz

er

Debuta

niz

er

C3

Acety

lene

Con

vert

er

Ethylene

Propylene

Hydrogen

Methane

Pyrolysis

Gasoline

Pyrolysis

Fuel Oil

Ethane

Propane

TLE and Oil

Quench

Primary

fractionation

Acid-gas

removal

Dilu

tio

n s

tea

m

Compression

C2

Acety

lene

Con

vert

er

Deeth

aniz

er

Feedstocks

Ethane

Propane

Butane

Naphta

Gas oil

C2

Split

ter

C3

Split

ter

Ma

in W

ash

Rectifie

r

After

Wa

sh

C4 fraction

Raffinate-1

Butadiene

Solv. makeup

Purification

Solvent

Focus on ethylene and butadiene separation

Ethylene separation

VLE diagram ethylene/ethane

20 bar

Low relative

volatility

High Ethylene

recovery

(> 99.99 %)

�Many trays

� Tall columns (expensive!)

�Ethylene/Ethane boiling point at 1 atm (-103.6 oC/-89 oC)

� Need to operate at high pressure (20 bar)

� Upstream compression

� Special materials needed

�High reflux ratios

� Large refrigeration duty (at -35 oC)

� Large operating cost (!)

High Ethylene purity

(~ 99.95 wt%)

Requirement 1

Requirement 2

Conventional vs Hybrid process

Compression: 11.7 MWe

Diameter: 3.65 m

Base case

18 % Lower condenser duty !

Compression: 9.6 MWe

Diameter: 3.31 m

Hybrid process

Simulation results

Electricity used Base case

(distillation)

Hybrid process

(membrane + distillation)

Condenser column, MW 11.7 9.6

Compression, MW 0 1.4

Compressor cooler, MW 0 0.8

TOTAL 11.7 11.8

Reflux ratio, [-] 4.23 3.41

Column diameter, m 3.65 3.31

Ethylene capacity, kt/yr 460 460

3.65

560

An increase in ethylene production capacity with 22 %

Sensitivity of membrane performance

The highest reported selectivity for a non facilitated

membrane is 12.

Sensitivity of membrane performance

Net profit 255 Euro/ton ethylene1

Ethylene market price ~ 795 Euro/ton

or 32 % from ethylene market price

Assumptions:

More details can be found in Motelica et.al., Ind. Eng. Chem. Res., 2012, 51, p.6977

Summary EE Separation

• In retrofit applications the hybrid process is technically and economically

feasible, when C2H4/C2H6 selectivity is > 10, and C2H6 permeance is ≥

1.6·10-9 mol·Pa-1·m-2·s-1

• Growth in ethylene demand requires debottlenecking of C2 splitter, which

is a major issue in a olefin plant.

• Membrane technology is very promising in debottlenecking a C2 splitter or

lower the investments for green field plants.

• Membranes can bring energy savings in a C2 splitter only if

ethylene/ethane membrane selectivity is > 60.

Alternative adsorption technology

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 1 2 3 4 5 6 7 8

Ad

sorp

tio

n P

ay

Ba

ck P

eri

od

, y

r

C2H6 removal rate, mol/kg/hr

Adsorbent 130 euro/kg

Adsorbent 500 euro/kg

Boost in ethylene capacity with 15 %

Butadiene separation

BASF NMP process (conventional)

Source: http://www.lurgi.info/website/index.php?id=55&L=1

Feed composition

Chemical structure Name Boiling

point, oC Composition,

wt%

Methyl Acetylene -23.02 0.2

iso-Butylene -6.9 26.4

1-Butene

-6.3 14.2

1,3-Butadiene -4.4 45.7

n-Butane -0.5 3.2

trans-2-Butene 1 5.1

cis-2-Butene 4 4.4

Vinyl acetylene 5 0.7

Ethyl acetylene 8.08 0.2

HC C CH3

CH3

C

H3C CH2

H2C

HC

CH2

CH3

H2C

HC

CH

CH2

H3C

H2C

CH2

CH3

H3C

HC

CH

CH3

HC CH

H3C CH3

H2C

CH

C

CH

H3C

CH2

C

CH

Distillation

Data based on Bohner et al., (2007) and Lurgi brochure

Chemical structure Component Name

Bunsen solubility, m3gas/m3 liq

Experiment1 Calculated

n-Butane 9.5 10.8

i-Butylene 15.42 13.2

1-Butene 15.6 17.9

trans-2-Butene 20.4 23.4

cis-2-Butene 25.1 28.8

1,3-Butadiene 41.5 42.3

Methyl-Acetylene 43 49.2

Ethyl acetylene 102 116.9

Vinylacetylene 226 258.9

H3C

H2C

CH2

CH3

CH3

C

H3C CH2

H2C

HC

CH2

CH3

H3C

HC

CH

CH3

HC CH

H3C CH3

H2C

HC

CH

CH2

HC C CH3

H3C

CH2

C

CH

H2C

CH

C

CH

Extractive Distillation

(1) Data from Wagner & Weitz (1970) ; Solubility is in pure NMP

Sat

Mono

Di &

Ace

Solv

ent re

cyclin

g

Simplified process

Design Specifications:

• 2000 ppmw butadiene in Raffinat 1

• 97wt% butadiene in side stream of Rectifier

• 0.005 kg/kg butadiene recovery (Rectifier Bottom)

• 0.05 kg/kg of Vinyl Acetylene recovery (After Wash Bottom)

100 kt/yr

45 34

20

25

Results of simulations:

33.6 MW of steam at 190 oC

or 9.75 GJ/ton butadiene

or 4020 Nm3/hr of natural gas

Chemical structure Component name Permeance, x 10-8 mol/(Pa·m2·s)

Vinyl acetylene

7.5 60 Ethyl acetylene

Methyl-Acetylene

1,3-Butadiene

cis-2-Butene

1 1

trans-2-Butene

1-Butene

i-Butylene

n-Butane 0.5 0.5

Selectivity (Di-Olefins/Saturated C4) 15 120

H2C

CH

C

CH

H3C

CH2

C

CH

HC C CH3

H2C

HC

CH

CH2

HC CH

H3C CH3

H3C

HC

CH

CH3

H2C

HC

CH2

CH3

CH3

C

H3C CH2

H3C

H2C

CH2

CH3

Component permeances

C4

Ace

tyle

ne

s&

Di-

ole

fin

s

C4

Mo

no

-ole

fin

sS

atu

rate

d

hy

dro

carb

on

s

Pe

rme

ate

Re

ten

tate

More details can be found in Motelica et.al., Ind. Eng. Chem. Res. 2012, 51, p.6977

Separation

challenge by

membrane is di-

olefins from mono-

olefins

Process Integration Options

Results process integration

Selectivity (Di-/Sat-) 15 60

Best process option from energy savings point of view B A

Energy savings (relative to base case) 23 % 30 %

Primary energy savings, GJ/ton butadiene 2.2 3.0

Potential savings in The Netherlands, PJ/yr 0.9 1.2

Summary Butadiene Separation

• High membrane selectivity are beneficial, however depending on the

process configuration, this does not lead always to significant benefits

(upper limit of Butadiene/Mono-olefins is around 60).

• Use of membranes with current extraction technology can lead up to 30%

in energy savings .

• Required membrane selectivity:

- Butadiene / Mono-olefins ≥ 7.5 or

- Butadiene / Saturated hydrocarbons ≥ 15

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